This follows the other examples so that it can be used as a tutorial,
such as the ones at:
https://developers.google.com/protocol-buffers/docs/tutorials
Even though Go generally does not use Makefiles, I added targets for the
Go examples to be consistent with the other languages.
Edit:
Fix Travis run. Change to use $HOME instead of ~. Add protoc to path.
GOPATH entry cannot start with shell metacharacter '~': "~/gocode"
Edit(2):
Fix Go code style to address comments.
